Mask off the least significant bit. in C, for instance: /* return 0 if even or 1 if odd */ char isOdd(char c) { return c & 0x01; } One side note... there is a whole class of problems that are slightly less trivial, such as determining if a character is uppercase or a character is a vowel or what-not. Brute force is your friend here, and the quickest way to do this is to come up with a table for your character set (not always 8 bits) that is a truth table for all combinations. You are sacrificing space for speed.